The present invention is directed internal bicycle hub transmissions and, more particularly, to an internal hub transmission which uses a sealing assembly that rotates with the hub shell.
Bicycles, particularly recreational bicycles referred to as city cruisers, are inexpensive and are easy to ride, and are thus widely used to commute to work or school or for shopping. With this type of recreational bicycle, an internal hub transmission is sometimes mounted at the rear wheel in order to ride at high speeds over flat terrain or to ride uphill with minimal exertion.
An internal hub transmission generally comprises a hub axle that is fixed to the bicycle frame; a hub shell that is able to rotate around the hub axle; a driving member for receiving a driving force from the drive chain; a planet gear mechanism that is housed in the hub shell for transmitting the driving force from the driving member to the hub shell through a plurality of transmission paths; and a clutch mechanism for selecting among the plurality of transmission paths. The clutch mechanism has a clutch member for switching the drive transmission path by moving in the direction of the hub axis, and a push rod that presses the clutch member.
Because the driving member and hub shell are capable of rotation relative to each other, there is a space between the two which creates a risk that water, dirt and other contaminants may enter the inside of the hub shell and adversely affect the operation of the planet gear mechanism and other components. Some internal hub transmissions use a labyrinth-type sealing mechanism to inhibit entry of contaminants into the hub shell. However, since such a system relies on staggered barrier walls with spaces between the barrier walls, there is still a risk that contaminants can migrate between the barrier walls and enter the inside of the hub shell, especially if the hub is immersed in water. Other internal transmission hubs use a rubber seal mounted to an inner peripheral surface of an annular metal ring which, in turn, is press-fit onto the inner peripheral surface of the hub shell. While such a sealing mechanism is effective, the rubber seal inevitably becomes worn as a result of the sliding contact with the driving member as the hub rotates relative to the driving member. Because the annular ring containing the rubber seal is press-fit onto the inner peripheral surface of the hub shell, removal of the old seal and installation of a new seal is very difficult. Thus, it is desirable to have a sealing system with the sealing characteristics of a rubber seal but which can be removed and replaced easily.